In this paper, we analyze the baroclinic Rossby radius of deformation which is a fundamental term in oceanography. We also discuss the story of the term's origin. The concept is found in the works by Bjerknes (1937) who was the first researcher to connect the dynamic characteristics of particles and the radius of surface curvature in synoptic structures. However, the analysis of dynamical equations by Bjerknes has rather a qualitative nature and refers to the atmosphere. This approach was further developed in the works by Carl Rossby who formulated it through the movement equations (Rossby, 1940). We also consider various approaches to numerical estimates of the deformation radius. Based on the ARMOR3D dataset, estimates of the baroclinic deformation radius for the Norwegian and the Greenland Seas are obtained and their spatial distribution is considered. The seasonal and interannual variability of the deformation radius is analyzed. It is shown that the Rossby radius in the studied area does not exceed 7-9 km on average. For most of the study area, the seasonal fluctuations in the radius are 1-2 km, with the greatest values of the radius being achieved in the warm season, and the smallest in the cold one. It was shown that bottom topography and convective processes play a significant role in the spatial and seasonal distribution of the Rossby deformation radius. An increase in both average and maximum values was revealed by the end of the 1993-2018 period.